Metal composite and method for filling a dental cavity in the preparation of a dental restoration

ABSTRACT

A metal composite and method for filling a dental cavity independent of cavity size. The dental metal composite comprises high-fusing temperature particles, low-fusing temperature particles, and a wax binder, and is inserted into the cavity to replicate the cavity, removed for heat treatment, densified, and reinserted to complete the filling operation.

FIELD OF THE INVENTION

This invention relates to a metal composite and method for filling adental cavity in the preparation of a dental restoration.

BACKGROUND OF THE INVENTION

Historically, a cavity in a vital tooth has been filled using either agold filling or an amalgam of silver and mercury. Concern over thepotential health hazard from the use of mercury in dental fillings hascreated a need for a substitute dental filling material and/or methodfor filling teeth using a filling material which does not containmercury. Ceramic materials and composites have been investigated andare, to a limited extent, currently used as a substitute for the mercuryamalgam. The ceramic materials do not, however, form as durable or asstrong a filling in comparison to a mercury amalgam or a gold-basedmetal filling. For larger cavities, an inlay, partial veneer or fullveneer is usually indicated, and is almost exclusively fabricated withmetal. At present, the inlay preparation requires laboratory involvementsimilar to the effort and expense in making a full crown.

The procedure currently practiced for preparing an inlay, onlay, orveneer requires careful cavity preparation, followed by taking animpression of the cavity which is then forwarded to a dental laboratoryto prepare a casting in much the same manner as in the preparation of afull crown. The inlay or onlay may also result in an unsightlyexhibition of metal since it is difficult to form a coating of porcelainfor application to only a specific area or surface. Moreover, the inlaymay fit poorly if the casting does not accurately reproduce theanatomical contour of the cavity.

SUMMARY OF THE INVENTION

A metal composite has been discovered in accordance with the presentinvention suitable as a substitute for the mercury amalgam in filling adental cavity, and preferably in accordance with a novel direct-indirectfilling technique, which permits the metal composite to be used as auniversal filling material for small or large cavities, including thepreparation of inlays, onlays, or a veneer. The metal composite of thepresent invention is, preferably, inserted directly into the dentalcavity to form a replica of the anatomical contour of the cavity. Uponremoval from the cavity, the composite is heat treated to form a porousmetal sponge which is then filled with a filler material to form a solidstructure having the shape of the dental cavity, and reinserted into thedental cavity to complete the filling operation.

Broadly, the method of the present invention is a direct-indirecttechnique for filling a dental cavity in a vital or nonvital toothwithin the mouth of a dental patient, comprising the steps of:

forming a metal composite comprising particles of a high-fusingtemperature metal, particles of a low-fusing temperature metal, and abinder substantially of wax in a concentration of at least about thirtypercent (30%) by volume of said composite;

inserting the metal composite in situ, into the dental cavity;

compacting the composite in the cavity to form a shaped compositeconforming to the anatomical contour of the cavity;

removing the shaped composite from the cavity;

heat treating the shaped composite material at a temperature below themelting temperature of the high-fusing temperature metal particles, tovolatize said wax and to form a porous metal sponge having a void volumeof above at least thirty percent (30%);

adding a filler material into the porous metal sponge to fill the voidsfor forming a solidified structure; and

cementing the solidified structure into the dental cavity to completethe filling operation.

The present invention also relates to a metal composite for use as adental kit in filling a dental cavity, comprising a first dentalmaterial composed of particles of a high-fusing temperature metal,particles of a low-fusing temperature metal, and a binder substantiallyof wax in a concentration of at least about thirty percent (30%) byvolume of said dental material, and a second material having a meltingtemperature below the melting temperature of the high-fusing temperaturemetal particles and selected from the group consisting of preciousmetals, ceramics, and plastics, for filling the voids in said firstdental material formed upon heat treatment at a temperaturesubstantially equal to the melting temperature of the low-fusingparticles. The binder should, preferably, be nonaqueous and nonliquid,and may include additives selected from the group consisting of anelastomer, self-hardening plastic material and a photopolymerizablematerial responsive to light energy.

BRIEF DESCRIPTION OF THE DIAGRAMS

Other objects and advantages of the present invention will becomeapparent from the following detailed description of the invention whenread in conjunction with the accompanying drawings, of which:

FIG. 1 is an exploded view partially in perspective, showing a shapedmetal composite removed from a dental cavity of a molar tooth for heattreatment in the preparation of a filling in accordance with the presentinvention;

FIG. 2 is an end view of FIG. 1;

FIG. 3 shows an embodiment of the rod which may be used for removing thecomposite from the cavity;

FIG. 4 shows the dental composite of FIG. 1 surrounded by investmentmaterial in preparation for solidification following heat treatment;

FIG. 5 is a view similar to FIG. 4, illustrating one embodiment forsolidifying heat-treated composite material; and

FIG. 6 shows the solidified structure of FIG. 5 in the investmentmaterial.

DETAILED DESCRIPTION OF THE INVENTION

The dental material of the present invention comprises a composite ofmetal particles and a binder substantially of wax, based upon theteaching of Applicants's companion application, Ser. No. 801,028, filedon Dec. 2, 1991 now abandoned, and entitled "Moldable Dental Materialand Composite, " the disclosure of which is herein incorporated byreference. The dental material, as more fully described in the companionapplication, comprises a uniform mixture of high-fusing temperaturemetal particles, low-fusing temperature metal particles, and a binder ofwax. The binder, in accordance with the present invention, is preferablyformulated from a nonaqueous, nonliquid composition substantially ofwax. Additional additives or agents may be added to the wax informulating the binder to modify the physical characteristics of thecomposite so that it forms a moldable putty which will replicate thedental cavity upon insertion, and which is capable of removal from thecavity with minimal distortion.

The need for additives, if any, depends upon the complexity of thecavity geometry and the extent to which distortion is acceptable.However, for most typical dental filling operations, a binder, primarilyor solely, of wax should be adequate. The additives are intended torender the binder more elastic, with the option of increasing hardnessafter insertion into the cavity. Elasticity may be increased by using anadditive such as an elastomer, a synthetic rubber, gum, orpolysaccharide and, preferably, an additive selected from the groupconsisting of a butadiene or isoprene polymer, phenol formaldehyde,polychloroprene, and magnesium resinate. Other or alternative additivesmay also be included to increase the material hardness at roomtemperature, or by the application of light energy from a visible orultraviolet light. Well known photopolymerizable materials includedimethacrylate and diacrylate resins which respond to ultraviolet light,and urethanes formed from acrylated polyesters, such as bis-GMA, which,in conjunction with a photoinitiator, responds to visible light.Alternatively, a room temperature self-hardening plastic composition maybe used.

If an additive such as a light-activated material is added to thebinder, the binder should be exposed to light to cure the material.Self-hardening additives may be used to promote and accelerate arelative hardening of the binder, to facilitate removal of the compositefrom the cavity. The shaped composite should have enough elasticity toovercome small undercuts in the cavity. The additives should representno more than fifty percent (50%) of the total content of the binder.

It is also within the scope of the present invention to apply thehardening photopolymerizable composition to the occlusal surface of thefilled cavity, i.e., over the composite to form a coating or surfacelayer which will selectivity harden the occlusal surface of thecomposite before removal.

The concentration of the binder should represent at least about thirtypercent (30%) by volume of the composite material, and up toseventy-five percent (75%). The wax in the binder permits the compositeto be heat treated to form a porous metal sponge of interconnectedhigh-fusing temperature metal particles with a substantial network ofvoids uniformly distributed throughout the sponge-like structure, havinga void volume of at least thirty percent (30%) after heat treatment. Thewax composition may be selected from natural wax, mineral wax, organicwax, or a synthetic wax composition. The wax composition should berelatively soft and tacky, and should melt relatively cleanly withoutleaving a significant residue. The melting temperature of the wax mustbe below the melting temperature of the low-fusing temperature metalparticles. Moreover, the high- and low-fusing temperature metalparticles should combine readily with the wax at room temperature toform a mixture with a uniform distribution of metal particles in thewax. Alternatively, the wax can be heated and the particles added andmixed, to form a uniform distribution of metal particles.

The high-fusing temperature metal component of the composite may be of asingle metal or metal alloy, preferably of precious metals such asplatinum and palladium, in any desired proportion relative to eachother, with or without other constituents such as gold, silver, copper,magnesium, aluminum, zinc, gallium, indium, and other metals or elementsfrom the third, fourth, or fifth group of elements of the periodictable. Gold may be added to the high-fusing temperature metal componentto increase the affinity between the high-fusing temperature metalparticles and the low-fusing temperature metal particles. The shape ofthe high-fusing temperature metal particles in the composite is veryimportant to the formation of the porous structure upon heat treatment.At least a majority, and preferably all, of the high-fusing particlesshould be irregular in shape and, particularly in the shape offlake-like platelets. A spherical shape should be avoided.

The particles of low-fusing temperature metal are composed preferably ofgold or a gold alloy, with gold as the major constituent. The preferencefor gold as the major constituent of the low-fusing component is basedon its known characteristics of workability, biocompatibility,non-oxidizing properties, and color. The particles of high- andlow-fusing temperature metal should be selected with an average particlesize of between 2 to 80 microns, and preferably between 4 to 32 microns.The size of the particles of high-fusing temperature metal may vary inrange from a size equal to the size of the low-fusing particles to asize of up to ten times the size of the low-fusing metal particles. Thevolume relationship of the metals in the composite mixture should be ina range of from about fifteen (15%) to seventy-five percent (75%) of thelow-fusing component relative to the high-fusing component, andpreferably from thirty (30%) to sixty-five percent (65%). Thecomposition of the selected metal particles for the high- and low-fusingcomponents will determine the optimum volume ratio. The weight ratiowill vary with the specific gravity of the selected materials, asevidenced by the examples at the end of the specification.

The cavity (8), as shown in FIG. 1, may be formed in a single tooth (10)or may extend from or between one or more tooth surfaces, such as theocclusal, mesial, distal, buccal, or lingual surfaces of several teeth.Because of the high concentration of wax in the composite, it has aputty-like texture and will readily assume the geometry of the cavity(8) with minimal pressure. The shaped composite (11) is then removedfrom the cavity (8) by pulling it out with an instrument or by insertinga member (12), in the form of a rod, into the composite (11), as shownin FIGS. 1 and 2, to facilitate lifting the composite (11) from thecavity (8) of the tooth (10) without causing significant deformation.The rod-like member (12) may be of a metal or plastic composition, andmay be solid or hollow. The rod-like member (12) may have any desiredcross-sectional geometry, such as cylindrical or rectangular, and may be"U-shaped." The member (12) may also be formed with a hook or bend atone end (not shown), to assist in the removal of the composite.Alternatively, the embedded section of the member (12) may have aprotruding shoulder (13) of conical geometry, such as a chamferedflange, as shown in FIG. 3, to facilitate removal of the shapedcomposite (11).

Upon removal from the dental cavity, the shaped composite (11) is heattreated to form a porous metal structure having a void volume betweenthirty percent (30%) and eighty percent (80%). The size of the metalparticles, their ratio, and predominantly, the concentration of binderin the mixture of high- and low-fusing temperature metal particles willcontrol the void volume of the porous structure formed by heattreatment. A capillary network interconnecting the voids is also formedin the porous mass, which controls the absorption and accommodation ofthe added filler material to fill the voids after heat treatment. Theheat treatment must eliminate the wax in the binder, preferably withoutleaving a residue, and must be high enough in temperature to cause thelow-fusing particles to melt without melting the high-fusing particles.

The shaped composite (11) may be embedded in a conventional refractoryinvestment material, as shown in FIG. 4, during or before heattreatment, or may be heat treated as a free-standing body and surroundedby a refractory investment following heat treatment. Heat treating thedental composite in investment material simplifies filling the voids inthe porous structure following heat treatment. If heat treated as afree-standing body, it is preferred to cover the surfaces whichinterface with the cavity walls with an antiflux following heattreatment, as will be discussed hereafter. The heat treatment may itselfoccur in a furnace, over a flame, or by the application of a highfrequency source of energy, etc., provided it substantially eliminatesthe binder and substantially melts the low-fusing temperature metalparticles to produce a porous sponge having a high void volume, asheretofore explained. The heat treatment temperature is between 800° C.and 1200° C.

After heat treatment, a filler material is melted into the voids of theheat-treated porous structure to solidify the structure beforereinsertion into the dental cavity. The porous metal structure may bereshaped, if desired, to assure a proper fit in forming the final dentalrestoration, before the filler material is added. The filler materialmay be any suitable ceramic, polymeric, or metal composition, preferablya gold-based precious metal composition. The filler material may also bein the form of a matrix of particles of filler material, and may bemixed with a wax component to form a wax body, which is placed over theporous structure, as shown in FIG. 5, to simplify the filling operationpursuant to a second heat treatment at a suitable temperature below themelting temperature of the high-fusing metal particles. For a fillermaterial of metal or of metal alloy, the second heat treatmenttemperature may be substantially equal to or above the first heattreatment temperature. The second heat treatment causes the filler metalto melt into the porous sponge to fill the voids. It should be notedthat the first heat treatment forms metal joints connecting thehigh-fusing temperature particles together. The joints are formed of analloy of high- and low-fusing metals, i.e., due to diffusion andmigration from the high-fusing particles, which has a meltingtemperature above the low-fusing metal melting temperature. Accordingly,the second heat treatment will not melt the joints, even if it is equalto the first heat-treatment temperature. Once the porous structure isfilled and solidified, it is recovered from the investment, cleaned,and, if desired, polished. The filler material may be in any particulateform, as a solid, a gel, or a liquid. If the filler is a liquid or isliquified, a hollow member (12) may be used to introduce the fillermaterial into the porous sponge.

The member (12), which aids in the removal of the composite from thedental cavity, may also function as the filler metal during the secondheat treatment. In this instance, the member (12) should melt during thesecond heat treatment, but at a temperature higher than the firstheat-treatment temperature, so that the porous sponge structure ispermitted to form before the temperature is elevated to the secondheat-treatment temperature to melt the filler metal. The meltingtemperature of the filler metal must also be lower than the meltingtemperature of the high-fusing temperature metal particles. Thus, if theporous sponge structure is formed at 1000° C., the filler metal may havea melting temperature of, for example, between 1050° C. and 1150° C.

As earlier stated, the heat treatment of the metal and wax dentalcomposite after removal from the dental cavity may occur in investmentmaterial, as shown in FIG. 4, or with the dental composite as afree-standing body. If heat treated as a free-standing body, the metalporous sponge structure may then be densified in investment as afree-standing body or submerged into a bath of molten filler metal. Itis important that the voids of the porous metal structure be filled toform a solidified body without changing the exterior dimensions of theheat-treated composite structure (11), particularly on the surfaces (14)where it interfaces with the cavity walls. Otherwise, it will no longerhave the shape of the cavity (8) into which it is being reinserted tocomplete the filling. This may be prevented by covering thefree-standing composite (11) with a protective layer of antiflux. Asuitable antiflux material may be a ceramic or glass composition, oreven graphite. A preferred alternative is to use a premeasured amount offiller metal relative to the weight of the metal in the composite (11),so that no excess material will exude out from the surface of thefree-standing porous body during the second heat treatment. Once theamount is determined for a given predetermined weight of metalcomposite, which can be ascertained by trial and error or byexperimentation, it may be standardized for that weight, i.e., for astandard tooth size. A different amount will be required if the fillermetal composition is changed or for other filler materials, such as aceramic or polymeric material, and, of course, for other predeterminedmetal composite weights. The different metal composite weights cancorrespond to different size restorations or fillings. The solidifiedcomposite structure (15), as shown in FIG. 6, is identical in shape tothe shaped composite (11). The solidified composite structure (15) isthen removed from the investment and reinserted into the cavity usingany conventional dental cement.

What we claim is:
 1. A direct-indirect method for filling a dentalcavity in a vital or nonvital tooth within the mouth of a dentalpatient, comprising the steps of:forming a metal composite comprisingparticles of a high-fusing temperature metal, particles of a low-fusingtemperature metal, and a binder substantially of wax in a concentrationof at least thirty percent (30%) by volume of said composite; insertingthe metal composite in situ, into the dental cavity; compacting thecomposite in the cavity to form a shaped composite conforming to theanatomical contour of the cavity; removing the shaped composite from thecavity; heat treating the shaped composite at a temperature below themelting temperature of the high-fusing temperature metal particles, tovolatize said wax and to form a porous metal sponge having a void volumeof above at least thirty percent (30%); adding a filler material intothe porous metal sponge to fill the voids for forming a solidifiedstructure; and cementing the solidified structure into the dental cavityto complete the filling operation.
 2. A direct-indirect method, asdefined in claim 1, further comprising inserting a member into saidcomposite to facilitate its removal from the cavity.
 3. Adirect-indirect method, as defined in claim 2, wherein said member iscomposed of metal.
 4. A direct-indirect method, as defined in claim 3,wherein said metal member has a protruding shoulder to facilitateremoval of the shaped composite from the cavity.
 5. A direct-indirectmethod, as defined in claim 2, wherein said binder includes additivesselected from the group consisting of: elastomer(s), gum(s), syntheticrubber, self-hardening plastic(s) and photopolymerizable materials.
 6. Adirect-indirect method, as defined in claim 2, wherein aphotopolymerizable material is applied to the occlusal surface of saidshaped composite to form a hard coating upon application of lightenergy.
 7. A direct-indirect method, as defined in claim 2, wherein saidshaped composite is heat treated at a temperature between 800° C. and1200° C.
 8. A direct-indirect method, as defined in claim 7, whereinsaid shaped composite is heat treated in refractory investment material.9. A direct-indirect method, as defined in claim 7, wherein said shapedcomposite is heat treated as a free-standing body.
 10. A direct-indirectmethod, as defined in claim 2, wherein said filler material comprises amaterial selected from the group consisting of metal, ceramic, orplastic.
 11. A dental composite for use as a dental kit in filling adental cavity, comprising a first dental material composition composedof particles of a high-fusing temperature metal of irregular shape,particles of a low-fusing temperature metal, and a binder composedsubstantially of wax in a concentration of at least about thirty percent(30%) by volume of said dental composite, and a second material having amelting temperature below the melting temperature of said high-fusingtemperature metal particles and selected from the group consisting ofprecious metals, ceramics, and plastics, for filling the voids in saidfirst dental material formed upon heat treatment at a temperaturesubstantially equal to the melting temperature of said low-fusingtemperature metal.
 12. A dental composite, as defined in claim 11,wherein said high- and low-fusing temperature metal particles vary in asize range of between 2 to 80 microns.